#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define endl '\n'
const int N = 2e5 + 5;
const double eps = 1e-6;

int w0, w, m;
double f(double r) {
  double res = w0;
  rep(i, 1, m) res = res * (1 + r) - w;
  return res;
}
int sgn(double x) {
  if (x == 0.0)
    return 0;
  else if (x < 0)
    return -1;
  else
    return 1;
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> w0 >> w >> m;
  double x1 = 0.0, x2 = 3.1;
  int s1 = sgn(f(x1)), s2 = sgn(f(x2));
  while (x1 + eps <= x2) {
    double mid = (x1 + x2) / 2;
    int s3 = sgn(f(mid));
    if (s3 >= 0)
      x2 = mid;
    else
      x1 = mid;
  }
  cout << fixed << setprecision(1) << 100.0 * x2;
  return 0;
}